We correct an error in the proof of Lemma 2.4. The analysis of possible poles applies unchanged and shows that if L ( s , π ∞ ⊗ ω ∞ ) and L ( 1 − s , π ˜ ∞ ⊗ ω ∞ − 1 ) have a common pole, then x ( ω ) lies in a finite union of hyperplanes in H. Applying the affine transformation x ↦ M x + b ( ω ) and noting that b ( ω ) lies in the Z-linear span of finitely many vectors, we see that y ( ω ) lies in a finite union of sets of the form ( V + A ) ∩ Q n , where V ⊂ R n is a proper subspace and A ⊂ R n is a finitely generated subgroup. Applying the lemma below, we conclude that there is a non-negative integer m and non-zero vectors w 1 , ... , w m ∈ Z n such that w j · y ( ω ) ∈ Z holds for at least one j ⩽ m whenever L ( s , π ∞ ⊗ ω ∞ ) and L ( 1 − s , π ˜ ∞ ⊗ ω ∞ − 1 ) have a common pole, and the rest of the proof goes through as before. Lemma.Let r , s , n ∈ Z ⩾ 0 with n > r , and consider vectors u 1 , ... , u r , v 1 , ... , v s ∈ R n . Then there is a non-zero vector w ∈ Z n such that Proof.Let x = ( x 1 , ... , x n ) be a typical element of ( R u 1 + ⋯ + R u r + Z v 1 + ⋯ + Z v s ) ∩ Q n and choose a non-zero vector z = ( z 1 , ... , z n ) ∈ R n orthogonal to u 1 , ... , u r . Then Next, consider the group